Prof. Dr.-Ing. habil. Egon-Christian von Glasner

Tire Mechanics

Lecture

Contents

0226 / 1103

1. Fundamentals2. Requirements and evaluation criteria3. Safety aspects4. Cost effectiveness5. Comfort6. Adhesion performance6.1. Influence of surface pressure6.2. Forces acting on tires6.3. Tires on dry road surfaces6.3.1. Free rolling wheel subjected to slip angle6.3.2. Straight ahead rolling wheel while accelerating and decelerating6.3.3. Combination of slip angle and slip6.4. Tires on wet road surface6.5. Tires on wintry/icy road surfaces

0229 /0903

Tire Design Fundamentals

Interior insulating layerBead

Bead reinforcement

Bead core

Sidewall

Carcass

Intermediate plyBelt

Shoulder Running surface

0227 / 0802

The Tire - A Compromise (1)

Good damping characteristics

Excellent ride comfort

Low rolling resistance

Minimal heat up

Excellent adhesion on wetroad surface

Good cornering stability

Large volume

Low inflation pressureObtuse cord angle

Increased inflation pressureAcute cord angleBelt type

Thin sidewallMixture with marginal damping

Transversely situated tread lugsFine profileFlat, broad running surface

Higher inflation pressureAcute cord angle

Longitudinally orientated profileLow height/width ratioBroadened rim width

Limited high speed capacityIncreased substructure loading

Reduced service lifeIncreased heat-upLess sufficient cornering stability

Moderate springing characteristicsBad road surface contactMinimal service life

Marginal sidewall stiffnessMarginal adhesion on wet roads

Marginal smoothnessMarginal service lifeIncreased running noise

Marginal ride comfortMarginal springing characteristics

Increased shoulder loading

Requirements Tire Design Measures Trend

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The Tire - A Compromise (2)

Maximum service life

Operational safety at high speed

Rolling noise reduction

Driveability in winter

Off-roadcapacity

Increasing stiffness of running surfaceUniform surface pressure distribution

High-strength cord typesThin sidewallsAcute cord angleHeat resistant mixture

Circumferential-rib tread, no fine treadNo lateral cuttingRunning surface mixture with high damping

Massive bar winter tread profileSpikes

Big volumeLow inflation pressureMassive bar tread profileAdaptable carcass

Limited high speed capacityIncreased heat-upMarginal ride comfort

Flat spots after prolonged standstillMarginal ride comfort

Marginal adhesion when wet, snow and iceIncreased rolling resistance

Increased riding noiseDecreased service lifeLimited high speed capacity

Increased heat-upLimited high speed capacity

Requirements Tire Design Measures Trend

Safety

Economy

Maximum attainable comfort fordriver and load

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System ”Wheel/Tire” - Evaluation Criteria

Primary criteria

0231 / 0903

System “Wheel/Tire” - Tire Characteristics Influencing Safety

Safety criteria

Mechanical strength

Tire force fit

Adhesion on dry, wet and icy road surfaces, when decelerating and accelerating

Economic criteria

Service life

Rolling resistance

Dimension and weights

Tire/chain compatibility

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System “Wheel/Tire” - Tire Characteristics Influencing Economy

0233 / 0903

Influence of Inflation Pressure and Load on the Service Life of a Tire

Prozentsatzdes Luftdrucks der Beladung

10

20

30

40

50

60

70

80

90

100

30 40 50 60 70 80 90 100 110 120 130 140 150

Lauf

leis

tung

%

74

%

Lauf

leis

tung

Prozentsatz

7074

100

Percentageof inflation pressure of load

Serv

ice

life

0234 / 0903

Influence of Inflation Pressure on Fuel Consumption of Commercial Vehicles

Incr

ease

d fu

el c

onsu

mpt

ion

(mea

n va

lues

)

Vans and light trucks (<7,5 t) Heavy trucks (>7,5 t)Reduction of inflation pressure

Results from test vehicles 1996-2002

··

···

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System “Wheel/Tire” - Tire Characteristics Influencing Ride Comfort

Comfort criteria

Springing behavior

Response- and re-aligning behavior

Uniformity and running noise

Ease of assembly

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Radial Spring Stiffness of a Commercial Vehicle Tire

Spring stiffnessTire:

Slip angle

0236 /0903

Adhesion between Tire and Road Surface - Scope of Testing

- Straight-ahead rolling wheel while

accelerating and decelerating

- Tire on wintry/icy road surface

- Free rolling wheel under slip

- Forces acting on a tire- Influence of surface pressure

- Tire on wet road surface

- Tire on dry road surface

- Combination of slip angle and slip

Measuring axle

0237 / 0903

Tire Test Truck

0238 / 0903

Tire Test Stand

0239 / 0903

300

Coefficient of Adhesion in Dependence of Surface Pressure

0

1

100 300N/cm2

Surface pressure pm

N/cm2200

Commercial vehicles

Coe

ffici

ent o

f adh

esio

n k

Dry road surface

Passengercars

0,5

0240 / 0903

Forces Acting on Tires

B kN braking force f mm tire rebound forceM Nm re-alignment torqueMγ Nm camber torquen mm distance between resulting

force and vertical axispi bar tire inflationQ kN resulting forceR kN wheel loadrdyn mm dynamic tire radiusS kN lateral forcev0 km/h road speedα ° slip angleβ ° angle of resulting force Qγ ° camber angle

B SR

v0

R

B

QS

rdyn

Unit TermDimension

0241 / 0903

Tire Characteristics According to GoughLa

tera

l for

ce

Wheel load R

Re-aligning torque

Dry road surfaceSlip angle

Caster

0374/ 0903

Late

ral f

orce

Wheel load R = 40 kNDry road surface

Lateral Force/Slip Angle Characteristics

Speed = 40 km/h Inflation pressure = 7,75 bar

11 R 22.5

Slip angle

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Influence of Camber Angle on Lateral Forces

Late

ral f

orce

Wheel load

Camber angle

Dry road surface

Slip angle

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Influence of Tread Conditions on Lateral Forces

Tread conditionLa

tera

l for

ce

Dry road surface

Slip angle

0,1 0,2 0,3 0,4 0,5Slip λ

Bra

king

forc

e B

Michelin XZA

11 R 22.5pi = 7,75 barv0 = 60 km/h

0

10

20

30

40

kN

Wheel load R = 40 kN

0392/ 0903

Braking Force/Slip Characteristics

Dry road surface

0377/ 0903

Influence of Tire Inflation Pressure on Lateral and Braking Forces

Dry road surface

Bra

king

forc

e

Late

ral f

orce Wheel load R

Tire inflation pressure piTire inflation pressure pi

Slip Slip angle

Dry road surface

Wheel load

0378/ 0903

Influence of Camber Angle on Braking Forces

Tendenz

1 2 3 4 5 6 7 8 9 10

Schlupf

Bre

msk

raft

Sturzwinkel nimmt zu

0°

5°

Slip λ

Bre

msk

raft

B

5°

0°Tendency

Bra

king

fo

rce

Camber angle increases

Slip angle increases

Michelin XZA11 R 22.5

pi = 7,75 barR = 40 kN

v0 = 60 km/hdry road surface

0,1 0,2 0,3 0,4 0,5 Slip λ

Bra

king

forc

e B

0

10

20

30

40

kN

0379/ 0903

Influence of Slip Angle when Braking

0253 /0903

The Principle of Cooperation between Circumferential Forces, Lateral Forces, Slip Angle and Slip

Lateral force

Slip angleBraking force Driving force

Slip

Braking force

Michelin XZA

11 R 22.5pi = 7,75 bar

R = 40 kNv0 = 60 km/h

dry road surface

Braking force B

Late

ral f

orce

S

Slip angle α

0380/ 0903

Measured Tire Characteristics

Michelin XZA

11 R 22.5pi = 7,75 barv0 = 60 km/h

dry road surface

Braking force B

Late

ral f

orce

S

Wheel loadR = 40 kN

0381/ 0903

Envelope Curves for Maximum Possible Adhesion of a Tire with Wheel Load as Parameter

Contact Area of a Tire on a Wet Road Surface

0255 / 0903

Direction of traveln

Contact area for a dryroad surface

Water wedge

Contact area fora wet

road surface

Water depth increases

Slip(Slip angle)

Speed Tread depth

Bra

king

forc

e (L

ater

al fo

rce)

Bra

king

forc

e

Bra

king

forc

e0256 / 0802

Influence of Water Depth on Braking Force/Lateral Force - Characteristics

Water depth increases Water depth increases

0393 / 0903

Dependence of Adhesion Limits from Water Depth

Lateral force

Dry road surface

Water depth (mm) increases

0.5

1,01,5

Braking force B Driving force A

C

EB

E

C

B

F

E

DA

B

CF

ED

C

A B

0

0,1

0,2

0,3

0,4

0,5

Produkte A, B, C, D, E, F bestimmter Reifenhersteller

Kra

ftsch

lußb

eiw

ert

k

Dimensionen:175 R 14 185 R 14 215 R 14205 R 14

∆ ≈ 300 % ∆ ≈ 300 %B

F

E

Products A, B, C, D, E, F of certain tire manufacturers

Coe

ffici

ento

f adh

esio

nk

Test Conditions: Water depth 2mm, Speed 100km/h, Wheel load 2kN

Tire sizes:175 R 14 185 R 14 205 R 14 215 R 14

∆ ∼ 300 % ∆ ∼ 300 %

0258 / 0903

Aquaplaning Performance of Tires made by Different Manufacturers

0259 / 0903

Influence of Ice Temperature on Lateral Force Capacities

Eisoberflächentemperaturnimmt zu

Schräglaufwinkel

Seite

nkra

ft

-4°

-2°

-1°

0°

Geschwindigkeitnimmt zu

Eisoberflächentemperatur (fallend

Seite

nkra

ft

)

Ice surfacetemperature increases

Late

ral f

orce

S

Slip angle a

- 4°

- 2°

- 1°- 0°

Ice surface temperature ϑ

Road speed increasesLa

tera

l for

ce S